Do you have your Cart manager plugin activated? That sometimes conflicts with other plugins or settings and deactivating it is a workaround. Have you addedd any new plugins that might interfere? What changes have you made since it was last working properly?
As far as I can recall, I didn't change anything, all of a sudden, it stopped working.
The cart manager plugin is deactivated since a long time. I also tried to deactivate and then activate all the theme and plugins, and the result remains the same.